JP3263837B2 - Manufacturing method of hot-dip galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-dip galvanized steel sheet using pre-Ni plating.

[0002]

BACKGROUND OF THE INVENTION The present applicant has previously described a method for producing a hot-dip galvanized steel sheet using pre-Ni plating as disclosed in Japanese Patent Laid-Open No. 4-147.
No. 954 has already proposed this. This Japanese Patent Laid-Open No. 4
In the method described in JP-A-147954, Ni is plated at 0.2 to 2.0 g / m ^{2 on the} surface of the steel sheet, and then H ₂ is plated at 0.1 to 15 g.
30% to 430-500 ° C in a N ₂ atmosphere containing
After performing rapid heating at a rate of temperature rise of not less than ° C./sec, zinc plating is performed by dipping in a molten Zn bath containing 0.1 to 1.0% of Al without being exposed to the air. Usually, after hot-dip plating, the amount of adhesion is adjusted by gas wiping. Further, usually, gas or steam cooling is performed immediately after gas wiping to solidify the plating layer to prevent Zn from adhering to guide rolls and the like.

[0003]

Recently, in the field of building materials and civil engineering, there has been an increasing expectation for hot-dip Zn-coated steel sheets having excellent coating film adhesion and excellent adhesion of processed parts at low cost. Although the hot-dip galvanized steel sheet manufactured by the above proposed method is extremely excellent in the adhesion of the processed portion, the coating film adhesion,
In particular, since the coating film swelling property of the flaw is insufficient, improvement thereof has been desired.

Therefore, the present inventors reviewed the manufacturing conditions of the hot-dip Zn plating method using the pre-Ni plating method in the above proposed method and made various studies. After performing the hot-dip Zn plating, it is also possible to secure the coating film adhesion by alloying the plating layer using an alloying furnace similarly to the hot-dip Zn plating method by a normal non-oxidation-reduction method. A new alloying furnace is required, which is disadvantageous in terms of cost. Without using an alloying furnace, it is inexpensive, and has excellent coating adhesion and excellent plating adhesion in the processed part. Aimed to develop a method of manufacturing.

Accordingly, the present inventors have proposed the pre-N
In order to find a method for producing a hot-dip galvanized steel sheet with excellent coating film adhesion and excellent plating adhesion in the processed part while utilizing the features of the i-plating method, the thickness of the original sheet, the temperature of the pre-treatment hot plate, the temperature of the molten Zn
As a result of studying while paying attention to the Al concentration in the plating bath, the cooling conditions after the bathing of the hot-dip Zn plating bath, and the like, the present invention has been achieved.

According to the present invention, there is provided a hot-dip galvanizing method in which a plated layer is alloyed without using an alloying furnace which is disadvantageous in cost as described above to obtain excellent coating film adhesion and also excellent plating adhesion in a processed portion. It is an object of the present invention to provide a method for manufacturing a steel sheet.

[0007]

As a result of various studies, the present inventors have found that in the above-mentioned pre-Ni plating method, the thickness of the original plate is made to be a certain thickness or more, the pre-treatment heating temperature, the temperature in the Zn plating bath, Setting the Al concentration in a specific range;
After leaving the n-plating bath, it was confirmed that the plated layer was alloyed by naturally cooling.

Further, as a result of evaluating the structure and performance of the plating layer, it was confirmed that those having an Fe content of 5 to 14% in the plating layer had excellent performance in both coating film adhesion and plating adhesion in the processed portion. . That is, the gist of the present invention is:
After pre-Ni plating of 0.2 to 2.0 g / m ^{2 is} applied to the surface of a steel sheet having a thickness of 2.3 mm or more, the steel sheet is heated to 430 to 550 ° C. in a non-oxidizing or reducing atmosphere, and Al.
It is immersed in a Zn plating bath containing 1 to 0.4% to perform hot-dip Zn plating, and after gas wiping, is allowed to cool naturally, thereby alloying the plated layer, thereby reducing the Fe content in the plated layer to 5 to 14%. A method for producing a hot-dip galvanized steel sheet.

Hereinafter, the present invention will be specifically described based on experimental results. First, the present inventors plated a pre-Ni plating layer on a hot-rolled Al-killed steel sheet (SPHC) of 1.6 to 6.0 mm with 0.5 g / m ² , and then added 1% of H ₂ + N ₂ and O ₂ 6
In an atmosphere of 0 ppm, at a heating rate of 40 ° C./sec.
Heated to 80 ° C, immersed in a hot-dip Zn plating bath at 470 ° C containing 0.2% of Al for 3 seconds, adjusted the adhesion amount to 60 g / m ² by N ₂ gas wiping, allowed to cool naturally for 25 seconds, With respect to the hot-dip Zn-plated steel sheet produced by water cooling, the Fe content in the plating layer and the performance (coating adhesion, plating adhesion of the processed portion) were examined.

FIG. 1 shows the relationship between the thickness of the original sheet and the Fe content in the plating layer. FIG. 2 shows the relationship between the Fe content in the plating layer, the coating film adhesion, and the plating adhesion of the processed portion. In addition, as for coating film adhesion, ◎ (less than 2 mm), ○ (2 mm to 4 mm), depending on the degree of coating film bulging, after cross-cutting after chemical conversion treatment and ED coating, and after salt spray test (SST),
(less than 4 mm), Δ (less than 4 mm to 5 mm), and × (5 mm or more). Further, the plating adhesion of the processed portion was examined by a tape peeling test after bending at 60 ° V. The evaluation criteria were as follows, and a score of 3 or more was judged to be acceptable.

Rating 60 ° V bending tape test blackness (%) 5... Less than 20% 4... Less than 20 to 30 3.... Less than 30 to 40 2. Less than 1... 50% or more From FIG. 2, it can be seen from the results that the both performances are excellent when the Fe content in the plating layer is 5 to 14%.
If it exceeds 4%, the plating adhesion of the processed portion may deteriorate.

From FIG. 1, the alloying of the plating layer gradually progresses until the plate thickness of the original plate is 2.3 mm or more and 6 mm used in the experiment, and the Fe content shows the coating film adhesion and the plating adhesion of the processed part. It can be seen that the optimum range, which is excellent in both properties, is 5 to 14%. Next, the present inventors plated a pre-Ni plating layer on a 4.3 mm hot-rolled Al-killed steel plate (SPHC) at a rate of 0.5 g / m ^2, and then in an atmosphere of H ₂ 1% + N ₂ and O ₂ 60 ppm. , Heated to various temperatures at a heating rate of 40 ° C./sec, immersed in a hot-dip Zn plating bath at 450 ° C. containing 0.25% of Al for 3 sec, and 60 g by N ₂ gas wiping.
/ M ^2, and the Fe content in the plating layer was examined for the hot-dip galvanized steel sheet produced by naturally cooling for 25 seconds and then cooling with steam and water. FIG. 3 shows the results of the investigation. From FIG. 3, it is understood that the Fe% in the plating layer is optimal in the range of the heating plate temperature of 430 to 550 ° C.

Next, the inventors of the present invention have proposed a hot-rolled Al of 4.3 mm.
0.5g of pre-Ni plating layer on killed steel plate (SPHC)
/ M ² plating, H ₂ 1% + N ₂ , O ₂ 60ppm
Is heated to 480 ° C. at a temperature rising rate of 40 ° C./sec, immersed in a hot-dip Zn plating bath of various Al concentrations at 450 ° C. for 3 sec, and 60 g / m ₂ by N ₂ gas wiping.
^The amount of adhesion was adjusted to ^2, and after natural cooling for 25 seconds, steam-water cooling was performed to investigate the Fe content in the plating layer of the hot-dip Zn-coated steel sheet. FIG. 4 shows the results of the investigation. From FIG. 4, it is possible to secure 5 to 14% of Fe in the plating layer when the Al concentration is in the range of 0.1 to 0.4%, and when the Al concentration is less than 0.1%, alloying proceeds excessively and exceeds 0.4%. It turns out that alloying is insufficient.

Next, the present inventors investigated the relationship between the cooling time after wiping and the Fe content in the plating layer. As a result, for example, the plate thickness was 4.3 mm, Al in the bath was 0.25%, and the bath temperature was 450. ℃, the coating weight of 135 g / m ² , when the bath intrusion plate temperature is 500 ℃, it is allowed to cool for about 25 sec.
At 0 to 480 ° C., the Fe content in the plating layer becomes 5% in about 46 seconds, the plate thickness is large, the bath temperature in the bath is high, the Al concentration in the bath is low, and the bath temperature is high, the plating adhesion amount increases. It was found that the smaller the amount, the shorter the cooling time required to secure the Fe content of 5 to 14% in the plating layer.

A bath temperature of 430 to 550 ° C. and a Zn adhesion amount of 45 to 150 g / m 2, which are ordinary hot-dip plating conditions, are used.
² , the plate thickness of the present invention is 2.3 to 6.0 mm, and the heating temperature is 43.
If hot-dip plating is performed within the range of 0 to 550 ° C. and an Al concentration in the bath of 0.1 to 0.4%, even if the plating layer is allowed to cool naturally until complete solidification after gas wiping, Fe
It was found that the concentration did not exceed 14% and was 5% or more. Therefore, when there is no facility restriction downstream of the gas wiping, after hot-dip plating within the above-mentioned condition range, natural cooling may be performed until the plating layer is completely solidified.

Next, the present inventors made a study on a hot-rolled Al of 4.3 mm.
0.5g of pre-Ni plating layer on killed steel plate (SPHC)
And / m ² obtained by plating, to prepare those not Ni-plated, both in _{H 2 1% + N 2,} O 2 in 60ppm atmosphere, heated to 550 ° C. at a heating rate of 40 ° C. / sec, Al 0.25%, immersed in a hot-dip Zn plating bath at 450 ° C. for 3 sec, adjusted the adhesion amount to 60 g / m ² by N ₂ gas wiping, allowed to cool naturally for 25 sec, and then cooled by steam and water to produce hot-dip Zn plating Regarding the steel sheet, the difference in plating adhesion of the processed portion was examined.

As a result, when there is pre-Ni plating,
A rating of 5 according to the evaluation criteria described above, and no pre-Ni plating
If the rating is 2, the case with pre-Ni plating is better.
It was found that the adhesion was good. About Ni adhesion amount
0.2 to 2 g / m^TwoWas examined in the range of
The plating adhesion was all good. Also economical
From the viewpoint, Ni is 2 g / m2. ^TwoThe following is desirable.

Also, the pretreatment heating rate after pre-Ni plating
The effect of the temperature was also investigated,
Enclosed area for plating adhesion under 60 degree V bending condition
No major changes were seen. Even earlier
Regarding the atmosphere at the time of processing and heating, N_TwoH than atmosphere_Two
Containing N _TwoThe atmosphere is better in plating appearance
A trend was observed.

The above results have been described for the case of only the Zn plating bath, but the results were also obtained for those containing Ni, Mg, Sb, and Pb as alloying elements in the plating bath in a trace amount of 3% or less, alone or in combination. Was similar. The pretreatment heating method before hot-dip plating is not particularly limited, and various methods such as a method of directly energizing and heating a steel sheet and an induction heating method can be applied.

The Zn plating adhesion amount is 45 to 450 g.
/ M ² , but it is preferably 150 g / m ² or less from the viewpoint of workability. Regarding the bath temperature, a normal condition of 430 to 500 ° C. can be used regardless of whether the bath is a Zn bath or a case where Zn contains a trace amount of an alloy element. As the base steel sheet, not only Al-killed steel but also hot-rolled steel sheet and cold-rolled steel sheet such as Ti-added ultra-low C steel and Si-Mn high tensile steel sheet can be used.

When a process such as roll brush grinding, skin pass, or shot blasting is performed as a pretreatment on a steel sheet,
The alloying speed of the Zn plating layer is fast and uniform, which is more effective.

[0022]

The feature of the present invention resides in that a plating layer is alloyed by sensible heat using a thick steel plate, and no alloying furnace after plating is required. It is considered that the greater the thickness, the higher the sensible heat, and the longer the heat is retained, the more alloying of the plating layer proceeds.

It is also important to perform pre-Ni plating, in which Ni uniformly covers the surface of the base iron with a thin layer to prevent oxidation of the base iron, and has high activity of the base iron itself, and has an activity on the steel plate surface. In order for the points to be uniformly present and for Ni to react with Al in the bath to suppress the formation of a strong Fe-Al-based barrier layer, It is considered that the reactivity is improved.

Further, it is considered that Al in the bath has an effect on the thickness of the barrier layer in the Zn-Fe alloying reaction.

[0025]

EXAMPLES Table 1 shows the molten Zn obtained by the production method of the present invention.
An example of a sample of a plated steel sheet is shown. * Mark other than the present invention
This is a comparative material created by the manufacturing method. The substrate has a different thickness
An Al-killed hot rolled steel sheet was used. Pre-Ni
0.5g / m by electroplating in sulfuric acid acid bath^TwoDo
Heating rate 40 ° C / sec, pretreatment heating (O_Two60pp
m, H_Two1% + N_TwoAtmosphere) at different temperatures,
In each case, hot-dip plating is performed at a bath temperature of 450 ° C for 3 seconds.
N_TwoThe amount of adhesion is 60 g / m by gas wiping. ^Twoage,
After natural cooling, air-water cooling was performed to prepare a sample. Plating
Fe% in layer, plating adhesion of processed part and after ED coating
Adhesion of coating film at cross cut part (SST4W
(Star property) was evaluated. The evaluation criteria are as described above.
Was.

[0026]

[Table 1]

No. 1 in Table 1. 1-4, 6-10, 12-1
As shown in Nos. 5, 17 to 21, and 23, it is clear that a predetermined plating layer is obtained under the production conditions of the present invention, and that the coating film adhesion and the plating adhesion of the processed portion are excellent. In the case of deviating from the range of the present invention (No. 5, 11, 16, 22), the performance is inferior.

[0028]

As described above, according to the production method of the present invention, molten Zn having excellent coating film adhesion and plating adhesion of a processed portion is excellent.
Since the coated steel sheet can be obtained at low cost without using an alloying furnace, its industrial significance is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the thickness of an original sheet and the Fe content in a plating layer.

FIG. 2 is a diagram showing the relationship between the Fe content in a plating layer, coating film adhesion, and plating adhesion of a processed portion.

FIG. 3 is a diagram showing a relationship between a pretreatment heating temperature before entering a plating bath and an Fe content in a plating layer.

FIG. 4 is a diagram showing the relationship between the amount of Al in a plating bath and the Fe content in a plating layer.

────────────────────────────────────────────────── (5) References JP-A-4-333551 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (1)

(57) [Claims] 1. A steel sheet having a thickness of 2.3 mm or more is pre-coated with 0.2 to 2.0 g / m ² of pre-Ni plating, and then heated to 430 to 550 ° C. in a non-oxidizing or reducing atmosphere.
Immediately immersed in a Zn plating bath containing 0.1 to 0.4% of Al, hot-dip Zn-plated, gas-wiped, and then allowed to cool naturally to alloy the plated layer, thereby reducing the Fe content in the plated layer to 5%. A method for producing a hot-dip galvanized steel sheet, which is set to be about 14%.